Pressure switch with a plurality of snap acting metal diaphragms coated with metallic oxide

ABSTRACT

Plural snap-acting, pressure-responsive, metal diaphragms having dished portions which permit the diaphragms to move from one dished configuration to an inverted dished configuration with snap action are disposed in nested relation to each other in a pressure switch. When fluid pressures are applied to the nested diaphragms from one side thereof, the diaphragms retain their original dished configuration during variation of said fluid pressures over a selected pressure range. However, the diaphragms move together with snap action to their inverted dished configuration when said fluid pressures reach predetermined levels. The diaphragms have protective oxide surface coatings which prevent galling of one diaphragm by another during said snap-acting movement of the nested diaphragms whereby the diaphragms retain their pressure response characteristics over a long service life.

United States Patent [72] Inventors Peter O. Fiore 3,378,656 4/1968 Johnson 200/83 P Culllbfllfllld, FOREIGN PATENTS RObCl't Baboian, Allleboro, Mass. 1 8 t B [21] APP] No 10,554 Grea r1 am 2 0/83 B [22] Filed Feb. 11, 1970 Primary Examiner- Robert K. Schaefer [45] Patented June 15, 1971 Assistant Examiner-Robert A. Vanderhye 73 Assign Texas mn Incorporated AIt0rneys-Harold Levine, Edward J. Connors, J r., John A.

D ll T Haug, James P. McAndrews and Gerald B. E stein [54] PRESSURE SWITCH WITH A PLURALITY OF A BSTRACT: Plural snap-acting, pressure-responsive, metal SNAP ACTING METAL DIAPHRAGMS COATED d aphragms having dished port1ons which permit the WITH METALLIC OXIDE diaphragms to move from one dished configuration to an inverted dished configuration with snap action are disposed in 6 Claims, 2 Drawing Figs.

nested relation to each other in a pressure switch. When fluid [52] U.S. Cl 200/8313, pressures are applied to the nested diaphragms f one Side 92/103 337/320 thereof, the diaphragms retain their original dished configura- [51] [IELCI ..H0lh35/34 on during variation of Said fluid pressures over a Selected [50] 7 Field of Search 92/ 103 M, pressure "Inga However, the diaphragms move together with 103 R; 200/83 83 83 P; 73/279; 117/130; snap action to their inverted dished configuration when said 337/320 fluid pressures reach predetermined levels. The diaphragms have protective oxide surface coatings which prevent galling [56] References Cited of one diaphragm by another during said snap-acting move- UNITED STATES PATENTS ment of the nested diaphragms whereby the diaphragms retain l31,6 l 9/1872 Belfield 92/ 103 M X their pressure response characteristics over a long service life.

36 30- m i 1 Z8 34 l v 4 ill 72 74 I, I Hlii 54 i|| \\T [a PRESSURE SWITCH WITH A PLURALITY F SNAP ACTING METAL DIAPHRAGMS COATED WITH METALLIC OXIDE In known pressure switches, a snap-acting metal diaphragm used for detecting the presence of excessive fluid pressures has a dished or deformed portion which permits the diaphragm to move with snap-action from one dished configuration to an inverted dished configuration. The diaphragm is positioned in the switch to expose one side of the diaphragm to a fluid pressure, the diaphragm deformation being proportioned so that the diaphragm retains its original dished configuration under the application of selected fluid pressures but so that, when the applied fluid pressure increases to a selected level, the diaphragm moves with snap-action to its inverted dished configuration. Electrical switch means or the like are disposed in the pressure switch to be responsive to this snapacting movement of the diaphragm.

When such prior art switches are used in high-pressure applications, it is difficult to provide snap-acting diaphragms which are capable of retaining their original configuration under the substantial fluid pressures considered to be normal in these applications. If such switches were to incorporate a single metal diaphragm capable of retaining its original dished configuration under the normally high fluid pressure to which the diaphragm is exposed, the stress limits of the diaphragm material would tend to be exceeded during subsequent snapacting movement of the diaphragm in response to even higher fluid pressures. As a result, the diaphragm would display rapid loss of its pressure responsive characteristics and would tend to become cracked during use of the switch.

It has therefore been conventional in these known pressure switches to utilize a plurality of dished, snap-acting metal diaphragms when the switches are to be used in high-pressure applications. The plurality of dished or deformed diaphragms are disposed within a switch in nested relation to each other. When the nested diaphragms are then exposed to fluid pressure from one side thereof, the diaphragms cooperate to retain their original configuration under very substantial fluid pressures but are adapted to move together as a common diaphragm means to their inverted dished configuration in response to selected, higher, fluid pressure levels.

It has now been found that a pressure switch utilizing a plurality of nested, snap-acting metal diaphragms in this manner tends to display gradual variation in the pressure response characteristics of the diaphragms. It has further been found that this variation in pressure response is due in large measure to galling and scratching of one of the nested diaphragms by another of the diaphragms during snap-acting movement thereof. That is, it is found that relative movement occurs between the nested metal diaphragms as the diaphragms move from one dished configuration to an inverted dished configuration. The metal-to-metal contact between the nested diaphragms then causes galling of the diaphragm surfaces during this relative movement, the galling required to cause a significant variation in the pressure response of the diaphragms being relatively small.

It is an object of this invention to provide a novel and improved pressure switch; to provide such a switch which is especially adapted for use in high-pressure applications; to provide such a switch which utilizes a plurality of nested metal diaphragms therein; to provide such a pressure switch which is adapted to maintain its pressure response characteristics over a long service life; and to provide sucha switch which is of simple and inexpensive construction.

Other objects, advantages and details of the pressure switch of this invention appear in the following detailed description of preferred embodiments of the invention, the detailed description referring to the drawings in which:

FIG. I is a section view along the central axis of the pressure switch of this invention; and

FIG. 2 is a section'view to enlarged scale along the central axis of a snap-acting metal diaphragm used in the switch of FIG. 1.

Referring to the drawings, 10 in FIG. 1 illustrates the novel and improved pressure switch of this invention which is shown to incorporate upper and low casing members 12 and 14 formed of material such as stainless steel having suitable strength and corrosion resistance. The lower casing member 14 has a peripherally extended flange 16 which is aligned with and abutted against the lower portion of casing member 12 to permit positioning of the casing members in telescoped relation as shown in FIG. 1 and to permit securing of the casing member 14. to the member 12 by welding or the like as indicated at 18.

A flexible metal ring 20 is secured to the upper portion of the casing member 14, by welding as at 22 for example, so that the inner peripheralportion 24 of the ring 20 projects radially inward beyond the portion of the casing member 14 on which it is mounted, thereby to create an overhanging, movable, inner portion of the ring. A snap-acting diaphragm 26 having a dished-or deformed portion 28 is secured to the ring 20, by welding as indicated at 30 for example, and a second snap-acting diaphragm 32 having a dished or deformed portion 34, is welded to the diaphragm 26 and at 36. That is, the diaphragms 26 and 32 are disposed in nested relation to each other with each of the diaphragms being secured to the other diaphragm or to the ring 20 around the periphery of the diaphragm. As thus assembled, the casing members 12 and 14 define cavities or compartments 38 and 40 which are hermetically sealed from one another by welding of the diaphragms 26 and 32 to each other or to the ring 20 and by welding of the ring 20 to the casing member 14. It will'be understood that means other than welding can be used for securing and sealing the diaphragms, ring and casing member 14 together. Casing member 12 includes an orifice or port 42 which communicates with the interior of the compartment 38 and which serves as an inlet to admit fluid pressure into the compartment 38.

Received in threaded engagement with the casing member 14, on the interior surface of the member which defines cavity 40, is an annular ring member 44. A wall member 46 rests on the annular member 44, this wall member having a central aperture 48 and having a motion-transfer pin 50 of nonelectrically conducting ceramic material or the like slidably mounted on the aperture 48. The wall member 46 has a generally concave spherical surface 52 disposed in facing relation to the diaphragms 26 and 32 as shown in FIG. 1.

' As illustrated in FIG. 1, the compartment 40 defined by the casing member 14 encloses a switch mechanism generally designed by reference numeral 54. That is, a metallic header plate 56 having a pair of spaced apertures 58 and 60 therein is secured to the casing member 14, preferably by welding as indicated at 62, for enclosing and sealing the compartment 40. Electrically conductive terminal posts 64 and 66 extend through respective header apertures and are secured and hermetically sealed within the apertures by any conventional glass sealing means 68 or the like. Alternatively, where sealing of the switch mechanism 54 is not required, other means can be used for mounting the terminal posts 64 and 66. Terminal post 66 supports a fixed electrical contact 70 and terminal post 64 supports a cantilever-mounted, electrically conductive, metal spring element 72 which carries a movable contact 74 at the distal end of the spring. As illustrated, the spring 72 is normally disposed to be engaged by the motion-transfer pin 50 which extends between the spring and the nested diaphragms 26 and 32. As will be understood, the spring is adapted to move in response to movement of the motiontransfer pin to engage the movable contact with the fixed contact for closing an electrical circuit from the post 66, through the contacts 70 and 74, and the spring 72 to the terminal post 64.

In accordance with this invention, the nested diaphragms 26 and 32 are of novel construction. That is, as shown in FIG. 2 for example, the diaphragm 26 embodies a core diaphragm element 26.1 of stiffly resilient metal material such as stainless steel. In a typical embodiment of this invention, for example, the diaphragm 26 em bodies a 300 series or 400 series stainless steel such as Type 302 Stainless Steel having a nominal com-- tion which provides the diaphragm with the dished configuration shown in FIG. 2. The deformation of the core element is such that the diaphragm 26 retains the dished configuration of FIG. 2 while a selected fluid pressure or other force is applied to the convex side of the diaphragm but moves with snap-action to an inverted dished configuration when a selected greater force is, applied to the convex side of the diaphragm. As snap-acting metal diaphragms of this type are well known, the precise nature of the deformation of the diaphragm core element 26.1 is not further described herein and it will be understood that deformation of the diaphragm 26 to provide it with selected pressure response characteristics is performed in conventional manner.

In accordance with. this invention however, the diaphragm 26 further embodies protective oxide coatings 26.2 and 26.3 which are disposed on the broad concave and convex surfaces of the diaphragm core element 26.1. These protective coatings comprise oxides of metal materials embodied in the diaphragm core element 26.1 and are characterized by being of relatively uniform composition incorporating such metal oxides in relatively high oxidation states. The protective coatings are of substantial thickness, preferably greater than about 100 Angstrom units thickness, and are strongly adherent to the diaphragm core element 26.] such that the coatings remain strongly adhered to .the core element during heating of the diaphragm 26 over a wide temperature range and during the described snap-acting movement of the diaphragm. The coatings are smoothj and readily visible and,

where the diaphragm core elements are formed of stainless steel, are bluish-green in color. Such oxide coatings are readily formed on the stainless steel core element 26.1 in the manner described in the copending application Ser. No. 10,533, filed Feb. 1 l, 1970 by the present inventors, and assigned to the assignee of the present invention. In this regard, it will be understood that although the coatings 26.2 and 26.3 illustrated in FIG. 2 are shown to cover only the broad concave and convex surfaces of the diaphragm core element, the coatings can also cover the edges of the core element within the scope of this invention. As will be understood, the snap-acting diaphragm 32 also preferably embodies a core element of stainless steel or the like having the noted, protective oxide coatings formed on the broad surfaces of the core element.

In operation of the pressure switch 10 above described, the switch is positioned with respect to a pressurized fluid zone such that the port 42 of the switch communicates with the zone for exposing the diaphragms 26'and 32 to the fluid pressures in the zone. The diaphragms normally cooperate with each other to retain the dished diaphragm configurations illustrated in FIG. 1 during normal variations of fluid pressure in the zone but, when fluid pressure in the zone increases to selected, relatively higher, abnormal pressure levels, the diaphragms 26 and 32 move with snap-action to their inverted dished configuration. This snap-acting motion is then transmitted through the motion transfer pin 50 to the spring 72 for closing the contacts 74 and 70 to indicate that fluid pressure in the zone has reached said selected, abnormally high levels.

In accordance with this invention, the protective oxide coatings of the diaphragms 26 and 32 prevent any galling or abrasion of the surfaces of the metal core elements of the diaphragms such as might otherwise result from relative movement between the diaphragm during said snap-acting movement. ln'this way, the diaphragms 26 and 32 retain their pressure response characteristics over a long service life. That is, the diaphragms 26 and 32 continue to move with snap-action in the described manner in response to the occurrence of the same fluid pressure levels in the zone being monitored by the switch 10.

As will be understood, the diaphragms 26 and 32 are adapted to return to their original dished configuratiomeither in response to bias of the sprin 72 or in response to inherent properties of the diaphragms, w en the pressuresm the mom tored zone fall below selected pressure levels. In this regard,

the wall member v46 can be adjusted by means of thering 44 in the manner described in US. Pat. No. 3,378,656, issued to C. N. Johnson on Apr. 16, 1968, thereby to determine operating characteristics of the switch 10 .in' the manner therein described. p

It should be understood that although a particular. switch mechanism 54 has been described by way of-illustration, any conventional switch mechanism would be incorporated in the pressure switch within the scope of this invention. Further, although only two snap-acting diaphragms are shown in the illustrated embodiment of this invention, it will be understood that additional diaphragms could be nested with'the illustrated diaphragms 26 and 32 within the scope of this invention. This invention includes all modifications and equivalents of the illustrated embodiments of this inventions which fall within the scope of the appended claims.

We claim:

l. A pressure switch comprising a plurality of snap-acting diaphragms each having a deformed portion which provides said diaphragm with a dished configuration and which permits said diaphragm to move with snap-action to an inverted dished configuration in response to selected force thereon, means supporting said diaphragms in nested relation to each other to expose said diaphragms to fluid pressure force from one side thereof, and a switch mechanism responsive to snap-acting movement of said diaphragms for indicating the occurrence of said movement, said diaphragms each embodying a snap-acting metal diaphragm element having a deformed portion providing said diaphragm with said snap-acting properties, said diaphragms'having metal oxide coating means thereon protecting said metal elements from abrasion during said snap-acting movement;

2. A pressure switch as set forth in claim 1 wherein said snap-acting metal diaphragm elements are formed of stainless steel.

3. A pressure switch as set forth in claim 2 wherein each of i said snap-acting metal diaphragm elements has a protective diaphragms each having a deformed portion which provides said diaphragm with a dished configuration and which permits said diaphragm tomove with snap-action to an inverted dished configuration in response to selected force thereon, said diaphragms being secured in nested relation to each other to one of said casingmembers for sealing said cavities from one another and for exposing said diaphragms to force of fluid pressure in one of said cavities, a switch mechanism mounted in the other of said cavities to be responsive to snap-acting movement of said diaphragms for indicating the occurrence of said movement, said diaphragms each embodying a snap-acting metal diaphragm element, having a deformed portion providing said diaphragm with said snap-acting properties, said diaphragms each having a metal oxide coating thereon protecting said metal diaphragm elements from abrasion during said snap-acting movement.

5. A pressure switch as set forth in claim 4 wherein said snap-acting metal diaphragm elements are formed of stainless steel. I

6. A pressure switch as set forth in claim 2 wherein each of said snap-acting metal diaphragm elements has a protective metal oxide coating thereon of a thickness greater than about Angstrom units thickness. 

1. A pressure switch comprising a plurality of snap-acting diaphragms each having a deformed portion which provides said diaphragm with a dished configuration and which permits said diaphragm to move with snap-action to an inverted dished configuration in response to selected force thereon, means supporting said diaphragms in nested relation to each other to expose said diaphragms to fluid pressure force from one side thereof, and a switch mechanism responsive to snap-acting movement of said diaphragms for indicating the occurrence of said movement, said diaphragms each embodying a snap-acting metal diaphragm element having a deformed portion providing said diapHragm with said snap-acting properties, said diaphragms having metal oxide coating means thereon protecting said metal elements from abrasion during said snap-acting movement.
 2. A pressure switch as set forth in claim 1 wherein said snap-acting metal diaphragm elements are formed of stainless steel.
 3. A pressure switch as set forth in claim 2 wherein each of said snap-acting metal diaphragm elements has a protective metal oxide coating thereon of a thickness greater than about 100 Angstrom units thickness.
 4. A pressure switch comprising a pair of casing members defining a pair of switch cavities, a plurality of snap-acting diaphragms each having a deformed portion which provides said diaphragm with a dished configuration and which permits said diaphragm to move with snap-action to an inverted dished configuration in response to selected force thereon, said diaphragms being secured in nested relation to each other to one of said casing members for sealing said cavities from one another and for exposing said diaphragms to force of fluid pressure in one of said cavities, a switch mechanism mounted in the other of said cavities to be responsive to snap-acting movement of said diaphragms for indicating the occurrence of said movement, said diaphragms each embodying a snap-acting metal diaphragm element having a deformed portion providing said diaphragm with said snap-acting properties, said diaphragms each having a metal oxide coating thereon protecting said metal diaphragm elements from abrasion during said snap-acting movement.
 5. A pressure switch as set forth in claim 4 wherein said snap-acting metal diaphragm elements are formed of stainless steel.
 6. A pressure switch as set forth in claim 2 wherein each of said snap-acting metal diaphragm elements has a protective metal oxide coating thereon of a thickness greater than about 100 Angstrom units thickness. 